1. Field of the Invention
The present invention relates to a spread spectrum radio communication system and, in particular, to a technique for synchronization acquisition carried out between a transmitter and a receiver in a spread spectrum radio communication system, particularly in a CDMA (code division multiple access) mobile radio communication system.
2. Description of the Prior Art
The CDMA mobile radio communication system includes, like other mobile radio communication systems, a base station and a plurality of mobile stations in each of service areas which are monitored and controlled by the corresponding base stations. The base station constantly broadcasts information about communications, such as a radio logical channel structure, to the mobile stations located in the corresponding service area. The broadcast information is used by the mobile stations for communications with the base station. The base station transmits the broadcast information in the form of frames. Specifically, the base station divides the broadcast information into a plurality of data units in a given order and then adds preambles between the adjacent data units so as to form the frames each composed of the preamble and the data unit. The preamble is assigned a bit sequence for synchronization acquisition which is double-spread, while the data unit is single-spread. Since each frame has the double-spread bit sequence, the reliability of the synchronization acquisition is improved.
Since each of the data units includes unique data as described above, each mobile station is required to detect a position of each frame among the frames. For achieving this, it is necessary for the mobile station to read a serial number assigned to each of the frames after establishing the synchronization acquisition. The reading of the serial number from each of the frames requires error correction decoding which necessitates complicated calculations. As a result, the mobile station takes a long time from the synchronization acquisition to the detection of a position of each of the frames.
Therefore, it is an object of the present invention to provide an improved radio communication system.
It is another object of the present invention to provide an improved transmitter to be used in the foregoing radio communication system.
It is another object of the present invention to provide an improved receiver to be used in the foregoing radio communication system.
According to one aspect of the present invention, there is provided a radio communication system comprising a transmitter and a receiver, wherein the transmitter comprises a frame producing circuit which produces a long frame comprising a plurality of frames each including a first bit sequence, and a second bit sequence located at the head of the long frame, the first bit sequences and the second bit sequence each used for establishing synchronization between the transmitter and the receiver, and wherein the receiver comprises a synchronizing circuit which establishes synchronization of the long frame based on the second bit sequence.
It may be arranged that the transmitter further comprises a first spreading circuit which double-spreads the second bit sequence, and wherein the receiver further comprises a first despreading circuit which double-despreads the double-spread second bit sequence.
It may be arranged that the transmitter further comprises a second spreading circuit which double-spreads the first bit sequence, and wherein the receiver further comprises a second despreading circuit which double-despreads the double-spread first bit sequence.
It may be arranged that the second bit sequence comprises a plurality of third bit sequences.
It may be arranged that the second bit sequence comprises a plurality of bit sequences which mutually differ from each other.
It may be arranged that the transmitter further comprises an amplifying circuit which sets a transmission power of the second bit sequence to be greater than a transmission power of the other of the long frame.
According to another aspect of the present invention, there is provided a transmitter for use in a radio communication system for communication between the transmitter and a receiver, the transmitter comprising a frame producing circuit which produces a long frame comprising a plurality of frames each including a first bit sequence, and a second bit sequence located at the head of the long frame, the first bit sequences and the second bit sequence each used for establishing synchronization between the transmitter and the receiver.
According to another aspect of the present invention, there is provided a receiver for use in a radio communication system for communication between a transmitter and the receiver, wherein the transmitter comprises a frame producing circuit which produces a long frame comprising a plurality of frames each including a first bit sequence, and a second bit sequence located at the head of the long frame, the first bit sequences and the second bit sequence each used for establishing synchronization between the transmitter and the receiver, the receiver comprising a synchronizing circuit which establishes synchronization of the long frame based on the second bit sequence.